According to UL standards, you must have 1 spare digital receiver for how many active digital receivers?

The correct answer indicates that, according to UL (Underwriters Laboratories) standards, for every five active digital receivers, there should be at least one spare digital receiver available. This is an important requirement as it ensures that the alarm system remains operational even in the event that an active receiver fails. Spares are crucial for maintaining the reliability and effectiveness of alarm systems, especially in emergency situations where response times are critical.

UL standards for alarm systems are designed to ensure a high level of safety and effectiveness. The requirement of having one spare receiver for every five active receivers reflects a proactive approach to system management and reduces downtime. If a backup is not readily available, a failure in one of the active receivers could compromise the entire alarm system's functionality, posing security risks.

In this context, the other options suggest different ratios of spares to active receivers, which do not align with UL’s established criteria.